The present invention relates essentially to a method of extracting a solvent from a mixture of solvent and hydrocarbons without any outer heat supply.
It is also directed to a system or plant for carrying out or practicing the method.
A number of methods of and systems for liquid-liquid extraction with a solvent are already known which use solvents for separating families, groups or series of hydrocarbons. These methods and plants however are very much adversely affected by the power costs since it is necessary to subsequently separate the solvent from the extract and raffinate phases.
This ultimate separation always requires a heat supply from the outside to the process or the plant, that supply taking place at a high heat level thereby substantially increasing the costs as is well understandable.
There are thus known methods directed to collecting both extract-solvent and raffinate-solvent phases and heating them in a furnace or by an outer fluid to provide for the evaporation of the solvent and to bring the hydrocarbons to an adequate temperature in order to obtain a viscosity low enough to allow the elimination through stripping of the last traces of solvent.
There are also known more performing methods which carry out successive evaporations in an order of increasing pressures. With such methods, the solvent is flash-evaporated and used to heat the feed of the foregoing flash-evaporation so that it is possible to reduce by about 30% the heat supply from the outside.
These methods however exhibit a number of inconveniences.
They require the use of a source of outer heat (furnace or hot oil) which is at a very high temperature and their operation or working is very unstable since the least disturbance in the temperature or the output of the hot source would be reflected on the plant and put same severely out of order. Moreover, these known methods and plants are of a complicated practice and use and require stacks of heat exchangers and of columns requiring cumbersome or bulky and expensive structures lending themselves badly to the reconstruction of old plants.